The present invention relates to a vertebral fixator and more particularly to an intervertebral/intravertebral fixator which may include an artificial discal articulation forming a disc prosthesis.
To combat severe vertebral and distal instability, particularly as a result of degeneration, which shows up as pain and stiffness which may be accompanied by compression of the spinal nerves and/or spinal cord, it is known practice for fixator devices known as xe2x80x9ccagesxe2x80x9d to be introduced into the intervertebral space. These cages, which generally consist of a small, holed hollow cylinder, are implanted by conventional posterior spinal surgical routes and usually require a bone graft, particularly a self-graft, to fix them rigidly. Implantation by the posterior route is advantageous because this is a relatively minor surgical intervention well tolerated by patients, particularly the elderly, and well mastered by surgeons. The cages do, however, present major drawbacks. On the one hand, they achieve total rigidity between the two vertebral discs that they interconnect, consequently eliminating any mobility at this point. When the cages are implanted in a number of intervertebral spaces, the entire regional vertebral column looses its natural suppleness or flexibility. In this case, the discs of the adjacent vertebral stages are overloaded and, in turn, will require arthrodesis. On the other hand, the use of cages entails a bone graft or osteosynthesis to fix the cages in the intervertebral space and fuse the vertebrae. These cages rarely provide sufficient stability and entail the additional fixing of one or more bulky posterior arthrodeses (metal plates or rods) on the vertebral column, which are also often necessary to avoid immobilizing the patient after the operation. Furthermore, these cages do not enlarge the height of their intervertebral space as much as they could, because they are small and the grafted bone matter does not exert a force that separates the vertebrae.
WO 00/13620 describes a pair of cages each of which is formed of two half cages between which a deformable material with damping properties is located. These cages have the conventional drawbacks of cages are regards fixing and bone grafting or osteosynthesis.
It is also known practice for devices with articulation, known as artificial discs, generally consisting of curved (convex or concave) elements capable of sliding one with respect to the other to be introduced into the intervertebral space. These devices are not fixators and are therefore not generally effective against vertebral instabilities. Furthermore, their effectiveness as an articulation is limited over time, generally to a few years, because after a certain length of time the relative movement between the two elements is disturbed. What is more, the amount of mobility, the geometry and/or the dimensions of these devices are not adjustable, particularly during and after implantation, which means that anatomical tailoring is not possible. A major drawback of these devices also lies in the necessity to resort to implantation via a non-posterior route. For the elderly, this then is a very major surgical intervention.
By way of example, such implants are described in EP-A-0820731 and in the pending American application 09/200855 and its parent application 08/897673, the contents of which documents are incorporated herein by reference. Despite of the very attractive properties regarding the possibilities of damping or adjustment after implantation, such artificial discs exhibit the other drawbacks mentioned hereinabove. Other intervertebral prostheses exhibiting the same kinds of drawbacks are described in EP-A-0346269.
WO 94/04100 describes an intervertebral discal prosthesis equipped with means of attachment into the adjacent vertebral bodies but also entailing a difficult surgical approach and furthermore requiring the intervertebral space to be opened up significantly during the fitting operation.
There also exist vertebral prostheses whose role is not to form a disc but to replace one or more vertebrae, forming an arthrodesis thereat. An implant such as this is described, for example, in U.S. Pat. No. 5,236,460, which describes an axially expandable vertebral implant with spikes capable of penetrating the vertebral bodies upon expansion. These prostheses are obviously used in far more major operations than those aimed at replacing a disc between two vertebral bodies.
The object of the present invention is to provide a vertebral fixator which does not reproduce the aforementioned drawbacks.
In particular, the object of the present invention is to provide a vertebral fixator which provides perfect fixation without the need for a bone graft.
In particular, the object of the present invention is to provide a vertebral fixator which may include a discal articulation which can afford some mobility and/or viscoelasticity.
Another object of the present invention is to provide a vertebral fixator such as this which can preferably be implanted by a strictly posterior route.
A further object of the present invention is to provide a vertebral fixator such as this, in which the degree of discal articulation mobility can be adjusted before, during and/or after implantation of the fixator.
Another object of the present invention is to provide a vertebral fixator such as this which can be removed, if necessary, preferably using the same posterior surgical route.
A further object of the present invention is to provide an intervertebral fixator such as this which can be connected to posterior fixator devices implanted on the posterior sides of the vertebral column. Such posterior devices advantageously comprise the adjustable devices described in documents EP-0 820 731 and FR-98 05549.
The subject of the present invention is therefore a vertebral fixator intended to be implanted between two adjacent vertebrae and consisting of fixator elements arranged exclusively in the intervertebral space defined between the said vertebrae and of fixator members fixed to the inside of the said vertebrae.
Advantageously, the said fixator comprises one essentially rigid first element fixed to the articular face of one of the two vertebrae, and one essentially rigid second element fixed to the articular face of the other vertebra, the said essentially rigid first and second elements being connected by at least one intermediate element.
Advantageously, the said essentially rigid first and second elements are plates comprising holes, the said plates each being arranged in the intervertebral space against the articular face of a respective vertebra so that the fixation members such as rods or screws are passed through the said holes and fixed, particularly screwed, into the respective vertebra.
According to a particular embodiment of the invention, the fixation members are screwed by means of a rotary rod introduced approximately radially into the intervertebral space, a system of rotary gearwheels being provided to convert the approximately radial rotary movement of the rod into an approximately axial rotary movement of the fixation member.
As a preference, the axial length of the fixation members is greater than the axial dimension of the intervertebral space, so that each of the said fixation members is formed of at least two fixation member parts implanted in turn, the said at least two fixation member parts interconnecting, particularly by snap-fastening.
As a preference, the said intermediate element comprises at least one moving and/or deformable element allowing relative movement between the said first and second rigid elements, to form an artificial discal articulation.
As a preference, the said at least one moving and/or deformable element defines a viscoelasticity, preferably an adjustable one.
Advantageously, the said viscoelasticity is adjustable after the fixator has been implanted, particularly by means controlled remotely from the outside.
According to one embodiment of the invention, the said at least one moving and/or deformable element comprises a bellows filled with liquid, particularly with silicone oil.
Advantageously, there are at least two bellows separate from one another, each bellows being filled with a respective determined amount of liquid, particularly silicon oil.
As an alternative, there are at least two bellows joined together, particularly via a valve, so that the liquid can pass from one bellows to the other, and vice versa.
Advantageously, the said at least one bellows is filled with liquid before, during and/or after implantation of the fixator, it being possible for the amount of liquid to be modified at any time after the fixator has been implanted.
Advantageously, the said fixator is implanted in the intervertebral space and fixed to the vertebrae via the conventional posterior vertebral route.
Advantageously the shape and/or dimensions, particularly axial, of the fixator are adapted, during the implantation, to suit the dimensions, particularly axial, of the intervertebral space.
Advantageously, the said fixator is designed to increase the axial dimensions of the intervertebral space to the maximum desirable height.
Another subject of the present invention is a vertebral fixator system comprising at least two vertebral fixators as defined hereinabove.
As a preference, a respective vertebral space contains at least two vertebral fixators.
Advantageously, the said at least two vertebral fixators have complementing exterior shapes so that once they have been implanted, they together form a geometrically coherent entirety capable of filling almost all of the intervertebral space.
Vertebral fixators may well be arranged in at least two intervertebral spaces, particularly adjacent ones.
According to an advantageous alternative form of the invention, the said vertebral fixators are connected to a posterior arrangement of fixators which is implanted in the posterior part of the vertebral column.
As a preference, the said connection is made by means of rods connecting the posterior arrangement of fixators to the fixation members of the said vertebral fixators.
Advantageously, the vertebral fixator system forms a total functional vertebral prosthesis for at least one vertebral stage, designed to provide simultaneous fixation and mobility of the facetiary posterior articulations and of the discal anterior articulations.